The state of the art of water quality modeling is reviewed and the six most comprehensive of the available models for simulating most water quality indices, including temperature, dissolved oxygen, BOD, nutrients, algae and zooplankton are evaluated. Models simulating only the DO-BOD relationship were considered to be inadequate for water quality management purposes and were not reviewed. Research needs for water quality model refinement are discussed. The importance of obtaining data adequate in quantity and detail for testing of models is stressed. Model application and analysis of model output are discussed.